Spa tub



FIG. 1 is a perspective view showing the top and front of the spa tub, the rear and left and right sides being the same;

FIG. 2 is a top plan view of the spa tub of FIG. 1; and,

FIG. 3 is an elevation view of the front of the FIG. 1 spa tub, the rear and left and right sides being the same. 

The ornamental design for a spa tub, as shown and described. 